Mrs. Wiesner has the fate of her family firmly under control. In her cramped janitor's apartment, she toils for the happiness and future of her children, who are supposed to be better off one day. Her daughter Helen thinks she is happily married to an American millionaire. Their son Herbert has managed to pass his A-levels with great difficulty and, unfortunately for him, is supposed to study medicine. Only the youngest daughter goes her own way, working as a waitress and socializing with foreigners. Nevertheless, everything seems to be in perfect order for mother Wiesner: her husband, a streetcar driver for the public transport company, is to inaugurate the latest streetcar as the crowning glory of his career. But as life goes: Happiness cannot always be steered into predetermined paths and sometimes things turn out differently than you would wish. When Helen unexpectedly returns from America with her child, Mrs. Wiesner's happiness begins to fade.